The Experimental Study On Time-Dependent Fracture Process Of Three-point Bending Concrete Beam

The ultimate failure of concrete is caused by concrete cracking,so it is necessary to study the concrete cracks systematically.Subtle cracks have existed in the interface between aggregate and cement slurry in concrete before loading,because of the inherent physical properties of aggregate and cement slurry are different.With the continuous increase of concrete load grade and load holding time,subtle cracks in the concrete will continue to develop,and finally lead to the failure of concrete.At present,the research on the monotonous static load fracture of concrete is mature,but there are few studies on the time-dependent fracture process and its influencing factors.In this paper,the test object size of standard three point bending beam is S×D×B=800mm×200mm×100mm?S×D×B=1200mm×300mm×100mm?S×D×B=1600mm×400mm×100mm(For the convenience of marking,"TFS-height-load grade" is used to represent the following).The influence of parameters on the time-dependent fracture of concrete is studied by applying different load grades and sizes.1.Static fracture tests were carried out on specimens of different sizes under monotonic loading,and the maximum load,P-CMOD curve and crack growth were obtained.2.The relationship between crack mouth opening displacement and load holding time was obtained by applying equivalent constant load of 80%and 85%to specimens of different sizes.3.The crack expansion of concrete three-point bending beam specimens in time-dependent fracture test was monitored,and the development relationship between crack expansion value ?a(t)and load holding time t was obtained and analyzed.4.The parameters of the specimens in the monotonous static load fracture test and the time-dependent fracture test were analyzed and compared.5.The fracture energy Gf is obtained by calculating the work done by the external force.And the required parameters of the bilinear softening curve were obtained by force analysis of the specimens in critical state,and the time-dependent fracture linear softening curve was drawn.